Affiliation: Department of Entomology, College of Agriculture, University of Kentucky, Lexington, KY, USA.

ABSTRACTInsulin/IGF-1 signaling (IIS) has been well studied for its role in the control of life span extension and resistance to a variety of stresses. The Drosophila melanogaster insulin-like receptor (InR) mutant showed extended life span due to reduced juvenile hormone (JH) levels. However, little is known about the mechanism of cross talk between IIS and JH in regulation of life span extension and resistance to starvation. In the current study, we investigated the role of IIS and JH signaling in regulation of resistance to starvation. Reduction in JH biosynthesis, JH action, or insulin-like peptide 2 (ILP2) syntheses by RNA interference (RNAi)-aided knockdown in the expression of genes coding for juvenile hormone acid methyltransferase (JHAMT), methoprene-tolerant (Met), or ILP2 respectively decreased lipid and carbohydrate metabolism and extended the survival of starved beetles. Interestingly, the extension of life span could be restored by injection of bovine insulin into JHAMT RNAi beetles but not by application of JH III to ILP2 RNAi beetles. These data suggest that JH controls starvation resistance by regulating synthesis of ILP2. More importantly, JH regulates trehalose homeostasis, including trehalose transport and metabolism, and controls utilization of stored nutrients in starved adults.

pgen-1003535-g001: JH and insulin regulate starvation resistance.A. RNAi-aided knockdown in the expression of genes coding for JHAMT or Met extended the starvation survival. Percent beetles survived during starvation after injection of control malE, JHAMT, or Met dsRNA respectively into 40 newly emerged male adults are shown. Starvation survival was recorded from day 4 to day 14. B. RNAi-aided knockdown in the expression of genes coding for ILP2 extend starvation survival. Percent beetles survived during starvation after injection of control malE, ILP1, ILP2, ILP3, or ILP4 dsRNA respectively into 40 new emerged male adults are shown. Starvation survival was recorded from day 4 to day 14. C. Bovine insulin can rescue the starvation survival of JHAMT or ILP2 RNAi beetles. Percent beetles survived after injection of control malE, JHAMT, ILP2 dsRNA into day 0 male adults followed by injection of either 25 mM HEPES or 25 mM HEPES containing 10 mg/ml insulin into day 5 adults are shown. The starvation survival was recorded from day 9 to day 14. D. JH III rescues starvation survival in JHAMT but not in ILP2 RNAi beetles. Shown are percentages of beetles survived after injection of control malE, JHAMT, ILP2 dsRNA into day 0 male adults followed by topical application of either acetone or 10 mM JH III in acetone on days 3, 5, and 7. The starvation survival was recorded from day 9 to day 14.

Mentions:
To determine the role of JH in the survival of the starved T. castaneum, the newly emerged male adults were injected with malE (dsRNA prepared using a bacterial gene malE as a control), JHAMT (a key enzyme in JH synthesis), and Met (JH receptor). The control-starved beetles began to die on seventh day post-adult emergence (PAE), and all beetles died by the fourteenth day PAE. However, a block in JH synthesis or its action by knockdown in the expression of genes coding for JHAMT (mean survival 12.8 days) or Met (mean survival 12.7 days) extended survival of the starved beetles by one day (control mean survival 11.7 days, P = 0.00002 in log rank test, Fig. 1A).

pgen-1003535-g001: JH and insulin regulate starvation resistance.A. RNAi-aided knockdown in the expression of genes coding for JHAMT or Met extended the starvation survival. Percent beetles survived during starvation after injection of control malE, JHAMT, or Met dsRNA respectively into 40 newly emerged male adults are shown. Starvation survival was recorded from day 4 to day 14. B. RNAi-aided knockdown in the expression of genes coding for ILP2 extend starvation survival. Percent beetles survived during starvation after injection of control malE, ILP1, ILP2, ILP3, or ILP4 dsRNA respectively into 40 new emerged male adults are shown. Starvation survival was recorded from day 4 to day 14. C. Bovine insulin can rescue the starvation survival of JHAMT or ILP2 RNAi beetles. Percent beetles survived after injection of control malE, JHAMT, ILP2 dsRNA into day 0 male adults followed by injection of either 25 mM HEPES or 25 mM HEPES containing 10 mg/ml insulin into day 5 adults are shown. The starvation survival was recorded from day 9 to day 14. D. JH III rescues starvation survival in JHAMT but not in ILP2 RNAi beetles. Shown are percentages of beetles survived after injection of control malE, JHAMT, ILP2 dsRNA into day 0 male adults followed by topical application of either acetone or 10 mM JH III in acetone on days 3, 5, and 7. The starvation survival was recorded from day 9 to day 14.

Mentions:
To determine the role of JH in the survival of the starved T. castaneum, the newly emerged male adults were injected with malE (dsRNA prepared using a bacterial gene malE as a control), JHAMT (a key enzyme in JH synthesis), and Met (JH receptor). The control-starved beetles began to die on seventh day post-adult emergence (PAE), and all beetles died by the fourteenth day PAE. However, a block in JH synthesis or its action by knockdown in the expression of genes coding for JHAMT (mean survival 12.8 days) or Met (mean survival 12.7 days) extended survival of the starved beetles by one day (control mean survival 11.7 days, P = 0.00002 in log rank test, Fig. 1A).

Affiliation:
Department of Entomology, College of Agriculture, University of Kentucky, Lexington, KY, USA.

ABSTRACTInsulin/IGF-1 signaling (IIS) has been well studied for its role in the control of life span extension and resistance to a variety of stresses. The Drosophila melanogaster insulin-like receptor (InR) mutant showed extended life span due to reduced juvenile hormone (JH) levels. However, little is known about the mechanism of cross talk between IIS and JH in regulation of life span extension and resistance to starvation. In the current study, we investigated the role of IIS and JH signaling in regulation of resistance to starvation. Reduction in JH biosynthesis, JH action, or insulin-like peptide 2 (ILP2) syntheses by RNA interference (RNAi)-aided knockdown in the expression of genes coding for juvenile hormone acid methyltransferase (JHAMT), methoprene-tolerant (Met), or ILP2 respectively decreased lipid and carbohydrate metabolism and extended the survival of starved beetles. Interestingly, the extension of life span could be restored by injection of bovine insulin into JHAMT RNAi beetles but not by application of JH III to ILP2 RNAi beetles. These data suggest that JH controls starvation resistance by regulating synthesis of ILP2. More importantly, JH regulates trehalose homeostasis, including trehalose transport and metabolism, and controls utilization of stored nutrients in starved adults.